Screw and nut mechanism



Feb. 27, 1951 ENGH 2,543,100

SCREW AND NUT MECHANISM Filed Dec. 15, 1948 j 6 7 fizvzmiar 5 Aiiorzzeys Patented res. 27.1951

.PTENT OFFIQE 2,543,100 SCREW AND NUT MECHANISM Casper Ill. Engh, Fargo, N. Dak.

Application December 13, 1948, Serial No. 65,018

4 @lainz i This invention relates to lifting jacks such as are frequently used for raising motor vehicles or portions thereof.

It is a general object of the invention to provide a lifting jacl; which is vertically extensible and operated by screw threaded members wherein proper lubrication of the threads is provided for and wherein the threads themselves are so formed that they will to a great extent, cut down the amount of frictional drag imposed on the threads when the device is lifting a relatively heavy weight.

The above and other objects and advantages of the invention will more fully appear from the following description made in connection with the accompanying drawing wherein like reference characters refer to the same parts throughout the views, and, in which:

Figure 1 is a view partially in side elevation and partially in vertical section, of a form of the invention; and

Figure 2 is an enlarged fragmentary vertical sectional view through the screw thread unit.

The device shown in the drawing i cludes a post unit comprising an inner tubular member 3 and a telescoping outer tubular member l. The inner m inber is removably received in an opening 5 in the upper portion 5 of a post i. The post i is provided with a bottom plate 8 having an upwardly struck boss 5? over which the tubular znber is removably received. A plug it is .i. into the lower end of the section 3 above a point to which the boss ii extends.

The outer tubular section t relatively closely yet freely slidably fits about the inner section 3. Welded otherwise suitably secured to the upper end of the outer section it is a cover plate if ha ing an opening 52 in its center. Extending downwardly in the outer section 5 and into the inner section 3 is a rod it which has most of its length provided with threads Just above the u per end the threads i is a shoulder 55 and upon this shoulder rests a ball thrust bearing unit indicated. generally at The extreme upper end of the rod 53 extends through the opening 52 in the cover plate ii and is squared as at H to removably receive a wrench or handle it by means of which the rod can be rotated.

The threaded portion of the rod it extends through and interfits with an internally threaded plug it? which is welded or otherwise suitably secured in the upper portion of the inner tubular section It should be noted that the plug is has its upper ortion located a considerable distance below the upper end of the inner tubular section 3. This provides a chamber or pocket which is adapted to hold a lubricant 20 which is indicated by stippling in Figure 1. It is preferred that the lubricant be a grease having a uniform degree of hardness under considerable temperature ranges and that it be sufliciently hard so that it will not readily flow between themale and female threads of the rod l3 and the plug l9.

The outer tubular section 4 is provided with a hook-like bracket 25 having a split side 22 drawn together by a bolt 23 so that the bracket can be raised and lowered on the outer tubular section 4 when and if desired.

In Figure 2 an enlarged fragmentary detail of the thread arrangement is shown. The male threads are shown at I and the female threads at 25. It will be seen that the threads are rather loosely fitted so that a certain amount of lateral play is provided. The lower surface 26 of the male thread l4 constitutes the thrust transmitting surfaces of that thread. This surface is concave radially of the rod. l3 on which the thread is formed. The female thread 2 5 has a thrust transmitting surface 25 which is on the upper side i of the thread and contacts the convex surface 25 on the lower side of the male thread. The curvature of the convex surface 26 is sharper than that of the concave surface 25 so that there is relatively limited contact between the thrust transmitting surfaces 25 and 25 of the male and female threads respectively. It is also preferred that the rise of the curve of the concave thread surface 26 be approximately the same on either side of the low point of the curve and that the low point be approximately centered transversely of the thread and in a direction substantially radially of the rod l3.

By reason of this thread construction there is a minimum of drag between the cooperating thrust transmitting surfaces of the two threads M and 24 while at the same time the threads themselves can be built sufficiently strong to support heavy loads.

When the handle or wrench ii; is rotated to lift a load imposed on the bracket 2!, it is ordinarily difficult to start movement of the jack because of the frictional drag incident to conventional constructions. With the thread construction shown and described there is a minimum of frictional contact between the threads which are lubricated by the lubricant 2f! in the chamber at the top of the post. When this initial force is applied to the handle it, the initial object is to start rotation of the threaded rod 53. Since the handle it is opposite from the axis of rotation and extends only from one side of the axis, there is an unbalanced turning force applied. Consequently, the rod I3 will in some cases tend to tilt slightly relative to the internally threaded plug [9 due to the loose interfitting of the two threads. This tilting action is very slight but is present and causes the convex portion 26 of the male thread to ride upwardly slightly on the concave surface 25 of the female thread. This produces movement of one threaded member relative to the other, whereupon the rod 53 can be started on its rotational movement with a smaller applied force because the stationary inertia has been overcome. When the device is lifting lighter weights the convex screw surface A 26 will remain approximately centered in the concave surface 25, but even when heavier Weights are lifted a greater force is applied to the handle. There will be shifting of the rod i3 relative to the internally threaded plug E6 but the concavity 25 will constantly tend to return the convexity 26 to a centered position.

In order to permit the above described rocking motion of the threaded rod l3 it should be noted that the thrust bearing unit [6 is slightly spaced from the inner wall of the outer tubular member 1 and that the aperture 12 in the cover plate H at the upper end of the tubular member 4 is larger than the upper end of the rod I3.

Reference is again made to the lubricant chamber at the top of the post unit. There is not a great amount of lubricant required to keep the threaded rod !3 properly lubricated. The location of the plug 19 below the upper end of the inner tubular section 3 provides a space into which the lubricant can be contained in addition to the space between the upper end of the tubular section I3 and the thrust bearing unit it.

It should be noted that the lower end of the outer tubular section 4 will engage the top of a short sleeve section 3a which is fastened to the bottom of the tubular section 3 to prevent collapsing of the tubular sections 3 and 4 beyond that point. This will maintain a space between the lower side of the thrust bearing unit it and the upper end of the inner tubular section 3 so that a considerable amount of lubricant can be placed in the lubricant chamber and cannot be forced past the threads by complete collapsing of the jack post.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the various parts without departing from the scope of my invention.

What I claim is:

1. In a lifting jack, a post unit including a pair of sections, one of which is vertically movable relative to the other, said sections having respective interfitting male and female threaded portions, the thread on one of said portions having a concave thrust transmitting surface, the complementary thrust transmitting surface of the thread on the other threaded portion being in contact with only a part of said concave surface, said threaded portions having a loose fit, and said complementary surface being shiftable on said concave surface.

2. The structure in claim 1 and said concave surface having a substantially equal rise transversely thereof in opposite directions from its low point, whereby said female and male members will tend to automatically center themselves under an axle thrust.

3. In a lifting jack, a post unit including a pair of sections, one of which is vertically movable relative to the other, one of said sections having a female threaded portion, a male threaded portion operably fitting in said female section, the threads of said portions having adjacent thrust transmitting surfaces, the thrust transmitting surface of one threaded portion contacting the adjacent surface of the other threaded portion over a radial distance considerably less than the depths of said threads, and the thrust transmitting portion of one of said threaded portions being convex.

4. The structure set forth in claim 3 and the other threaded portion being concave, the convex threaded portion being on a sharper curve than the concave threaded portion.

CASPER H. ENGH.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,154,519 Lansdowne Sept. 21, 1915 1,810,910 Esmond June 23, 1931 2,215,107 Mulka Sept. 17, 1940 FOREIGN PATENTS Number Country Date 528,932 Great Britain Nov. 11, 1940 

